Trim articles with light stable covering containing invisible tear seam, and process of making the same

ABSTRACT

A panel structure is mountable in a vehicle to form a part of the interior thereof in concealing relation to a secondary restraint system. The novel panel structure of this invention includes a layered composite structure and a reinforcing substrate having a door structure movable through the layered composite structure upon the operation of the secondary restraint system. The layered composite structure includes an outer layer and an inner layer adhered to the outer layer, the inner layer including a seam-defining structure. In one embodiment, the seam-defining structure is a narrow elongated structure configured to define an exteriorly invisible tear seam generally corresponding with portions of an outline of the door structure, and the inner layer has a reduced thickness portion along the exteriorly invisible tear seam by virtue of the presence of the narrow elongated structure. In another embodiment, the seam-defining structure is a sheet structure severed to define an exteriorly invisible tear seam generally conforming to an outline of the movable door structure. The invisible tear seam defined by the narrow elongated structure or the severed sheet structure causes the layered composite structure to fracture generally along the invisible tear seam in response to the movement of the door structure through the layered composite structure during the operation of the secondary restraint system.

[0001] This application is a continuation of application Ser. No.09/394,032, filed Sep. 13, 1999, which in turn claims the benefit ofProvisional Application No. 60/100,124, filed on Sep. 14, 1998, theentire contents of which are incorporated herein by reference.

FIELD OF INVENTION

[0002] This invention relates to interior trim articles containing apanel structure mountable in a vehicle to form a part of the interiorthereof, and in particular to automobile interior trim articles, such asinstrument panels and door panels, which conceal a secondary restraintsystem including an air bag. This invention further relates to a processfor making the aforementioned interior trim articles.

BACKGROUND OF THE INVENTION

[0003] The escalation of the commercial significance of air bagrestraint systems in automobiles as secondary restraint systems hasmanifested itself in the appearance of air bag restraint systems inmany, if not most, new automobiles. The commercial impact of suchsecondary systems is attributable both to government regulations andconsumer demand for safety.

[0004] Generally, air bag restraint systems are concealed from viewduring normal operation of the vehicle by arranging the air bagrestraint systems behind automotive interior trim articles, such asinstrument panels and/or door panels.

[0005] In order to permit the deployment of the air bags upon collisionof the vehicle, interior trim articles are often formed with amulti-layered structure comprising a rigid substrate having hidden doorsformed therein, an outer decorative skin layer, and a soft cellularpolyurethane foam layer formed therebetween. The hidden doors of therigid substrate are configured and arranged in such a manner that theedges of the doors define discernible patterns, such as patterns in theform of H, C, U, and X shapes.

[0006] During deployment of the air bag, the air bag is actuated via agas generating system and expands from a folded, undeployed state to aninflated, deployed state. The expansion of the gas inflates the air bagagainst the backside of the hidden doors and forces the hidden doors toopen into the passengers' compartment of the vehicle. The emergence ofthe hidden doors into the passengers' compartment creates a passagewaywhich permits deployment of the air bag into the passengers' compartmentof the vehicle. The deployed air bag protects the driver and passengerfrom violent collision against the panel structure.

[0007] In order to minimize obstruction of the passageway through whichthe expanding air bag traverses, the underside of the outer skin can beprovided with structurally weakened tear seams. These tear seams oftentake the form of perforated or channel-like patterns, and areconstructed and arranged to substantially correspond to and overlay thepattern (e.g., H-shaped) defined by the edges of the hidden doors of thesubstrate. During deployment of the air bag, the outer skin tears orfractures along the structurally weakened tear seams. Absent thepresence of such structurally weakened tear seams in the outer skin, theouter skin may possess sufficient internal strength to resist fractureupon deployment of the rapidly expanding air bag. If the skin does notfracture, the entire outer skin can become separated from the rigidsubstrate and/or the multi-layered structure can be dismounted from thevehicle frame, thereby imperiling the safety of the driver andpassengers.

[0008] Different techniques have been proposed to form a multi-layeredstructure having an outer skin with a structurally weakened, rupturabletear seam. One conventional technique involves the preparation of arotational-cast poly(vinyl chloride) (“PVC”) skin by providing a powderbox including a seam-defining structure or gasket, which partitions thepowder box into two chambers. A PVC powder with appropriate colorantsand additives, such as plasticizers, is retained in each of thechambers. Where a dual-tone appearance is desired, the chambers can besupplied with PVC powders containing different colorants, in which casethe seam-defining structure simultaneously serves as a color divisionrim. The powder box is then engaged to a metal mold component to definea closed casting system having the seam-defining structure closelyspaced from a heated mold surface of the metal mold component. The PVCpowder is then tumbled against a heated molding surface of the metalmold by a rotational casting method until the PVC powder is formedagainst a moderately heated mold surface in a gelled state. Excesspowder collects in the powder box, and is thereafter separated andremoved from the mold. Since the seam-defining structure obstructs thegelling of PVC powder on the portion of the heated mold surfacetherebelow, the structurally weakened portion of the skin is formedbelow the seam-defining structure. A lower density or lower strengthtear seam material (also referred to as a filler material) is thensprayed into the perforated or channel-like seams and gelled. The gelledPVC material and the gelled tear seam material are then fused by heatingthe materials to their fusion temperatures, and thereafter cooled toprovide the PVC-based covering in a thermoplastic solid state. The skincan then be united with the rigid substrate, such that the low densitymaterial of the outer skin is positioned to substantially correspond toand overlay the edges of the hidden doors.

[0009] There are at least two problems associated with theabove-described conventional method. First, the presence of theseam-defining structure hinders the normal compacting of the PVC powderwhich occurs during rotation of the closed system. Hence, the portion ofthe skin layer corresponding to the structurally weakened tear seampossesses a greater porosity than the remainder of the skin. Thedifference in porosity between the structurally weakened portion and theremaining portion of the outer skin makes the pattern of the tear seamvisible, especially in bright light. The second problem is due to thedifference in composition of the cast skin and the sprayed tear seammaterial. In top-mount applications in which the tear seam is exposed tohigh temperatures and intense UV radiation, the sprayed materialintroduced into the tear seam ages differently than the surrounding castmaterial and will become clearly visible over time. For these reasons,multi-layered structures made by the aforementioned conventional methodare only effectively employed in mid mount applications where the hiddentear seam is not exposed to direct sunlight.

[0010] In order to overcome these problems, it has been proposed to forma PVC skin layer of uniform thickness, and thereafter form thestructurally-weakened tear seams by laser cutting the backside of theskin. Due to the relatively small thickness of the skin, however, it isvery difficult to precisely control the depth of the cut portion.Consequently, errors in laser cutting can lead to the disposal of skinsas unusable scrap. In addition, the capital investment associated withobtaining and operating a laser cutting apparatus is very high.

[0011] A need therefore exists to provide a process for making a panelstructure containing a decorative covering having an inner surface witha structurally weakened tear seam in which the tear seam is concealedfrom view, even after employing the covering in top mount applicationswhich subject the covering to prolonged use and exposure to hightemperatures and intense UV radiation.

SUMMARY OF THE INVENTION

[0012] The disadvantages of the prior art may be overcome by providing aprocess for making a panel structure comprising a layered compositestructure and a reinforcing substrate including a door structure movablethrough a portion of the layered composite structure upon the operationof the secondary restraint system. The panel structure is mountable to avehicle to form a part of the interior thereof in concealing relation toa secondary restraint system.

[0013] In accordance with one embodiment of this inventive process, thelayered composite structure is formed on a mold surface, the layeredcomposite structure comprising an outer layer with an exterior surfacehaving an opaque visual appearance, a seam defining structure configuredto define an exteriorly invisible tear seam generally corresponding withportions of an outline of the door structure movable through the layeredcomposite structure during the operation of the secondary restraintsystem, and an inner layer having a frangible line along the exteriorlyinvisible tear seam by virtue of the presence of the seam definingstructure. The layered composite structure is united with thereinforcing substrate so that the reinforcing substrate reinforces thelayered composite structure in such a way that the narrow elongatedstructure and the reduced thickness portion of the inner layer along theinvisible tear seam causes the layered composite structure to fracturegenerally along the invisible tear seam in response to the movement ofthe door structure through the layered composite structure during theoperation of the secondary restraint system. Optionally, a soft cellularfoam layer can be interposed between the layered composite structure andthe reinforcing substrate.

[0014] In accordance with another embodiment of this inventive process,the layered composite structure is formed on a mold surface andcomprises an outer layer with an exterior surface having an opaquevisual appearance and an inner layer adhered to the outer layer andincluding a seam defining structure in the form of a severed sheetstructure through which the door structure moves during the operation ofthe secondary restraint system. The layered composite structure and thesubstrate are united so that the substrate reinforces the layeredcomposite structure. The sheet structure is severed to define anexteriorly invisible tear seam generally corresponding with portions ofan outline of the door structure. The severed portion defining theinvisible tear seam causes the layered composite structure to fracturegenerally along the invisible tear seam in response to the movement ofthe door structure through the layered composite structure during theoperation of the secondary restraint system. A soft cellular foam layeroptionally can be interposed between the layered composite structure andthe reinforcing substrate.

[0015] Other objects of the invention are achieved by providing anarticle comprising a panel structure made by the above-mentionedembodiments of the inventive process of this invention.

[0016] Since the layered composite structures provided in accordancewith the above-discussed embodiments have an outer layer that can beuniformly sprayed onto heated mold surface without requiring aseam-defining structure for forming a structurally weakened seam in theouter layer, the outer layer of the composite structure does not exhibitthe non-uniform porosity that characterizes conventional skins. Further,the outer layer assists in masking and concealing the non-uniformporosity and/or differentials in aging between the portion of thelayered composite structure defining the structurally weakened tearseam.

[0017] The layered composite structure of this invention also exhibitsexcellent chemical, scuff and mar resistance to external influences.Further, appropriate additives can be introduced into one or more of thelayers of the layered composite structure to provide the compositestructure with the non-reflective and low gloss surface appearancedesired for such panel-like structures. Furthermore, both the inner andouter layers of the layered composite structure are characterized byexcellent extensibility, such that the layered composite structure canwithstand indentation and flexure during use without resulting incracking in the outer layer over a wide temperature range, such as from−30EC to 120EC.

[0018] The principles of this invention enunciated above are applicableto all types of skinned panel structures through which an air bag mightdeploy, but have particular applicability to instrument panels (alsoreferred to as dashboards), door panels, steering wheels, pillar covers,headliners, and rear interior quarter panels. Moreover, the principlesof this invention are applicable to various types of automotivevehicles, including passenger cars, trucks, vans, utility vehicles, andothers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings illustrate this invention. A firstembodiment of the invention is illustrated in FIGS. 1-12, in which:

[0020]FIG. 1 is a perspective, partially phantomed view of a completedvehicle instrument panel constructed in accordance with a firstembodiment of this invention;

[0021]FIG. 2 is a sectional view of the instrument panel of a FIG. 1taken along line II-II;

[0022]FIG. 3 is a sectional view showing the air bag in a partiallyinflated deployment position;

[0023]FIG. 4 is a sectional view like FIG. 3, except showing the air bagin a fully inflated deployment position;

[0024]FIG. 5 is a sectional view of a mold surface showing a step ofapplying a water-dispersed polyurethane composition to a heated moldsurface to form a partially crosslinked light-stable polyurethane outerlayer;

[0025]FIG. 6 is a sectional view similar to FIG. 5 showing a step ofdrying the polyurethane outer layer;

[0026]FIG. 7 is a depiction of one construction and arrangement of anarrow elongated structure of the first embodiment;

[0027]FIG. 8 is a depiction of another construction and arrangement of anarrow elongated structure of the first embodiment;

[0028]FIG. 9 is a sectional view similar to FIG. 6 showing a layeredcomposite structure formed on the heated mold surface;

[0029]FIG. 10 is a sectional view similar to FIG. 9 showing a step ofremoving the layered composite structure from the mold surface;

[0030]FIG. 11 is a sectional view showing a step of depositing arelatively rigid polyurethane cellular foam intermediate layer on theinner layer while the layered composite structure is disposed on asecond mold surface; and

[0031]FIG. 12 is a sectional view showing a step of uniting the layeredcomposite structure on the second mold surface with a pre-formedrelatively rigid substrate disposed on a third mold surface.

[0032] A second embodiment of the invention is illustrated in FIGS.13-17, in which:

[0033]FIG. 13 is a perspective, partially phantomed view of a completedvehicle instrument panel constructed in accordance with a secondembodiment of this invention;

[0034]FIG. 14 is a sectional view of the instrument panel of a FIG. 13taken along line XIV-XIV;

[0035]FIG. 15 is a depiction of one construction and arrangement of athin sheet structure of the second embodiment;

[0036]FIG. 16 is a depiction of another construction and arrangement ofa thin sheet structure of the second embodiment;

[0037]FIG. 17 is a sectional view showing a step of uniting the layeredcomposite structure on the second mold surface with a pre-formedrelatively rigid substrate disposed on a third mold surface; and

[0038]FIG. 18 is a depiction of another construction and arrangement ofa thin sheet structure of the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0039] Referring now more particularly to the drawings, there is shownin FIG. 1 a panel structure comprising a vehicle instrument panel,generally designated by reference numeral 10, made by a method inaccordance with a first embodiment of this invention.

[0040] In this embodiment of the invention, the panel structure 10 isshown in a top mount position. The structure 10 includes pivotal doors12 having edges that define a hidden H-shaped pattern 14. In this topmount position, the panel structure 10 underlays a sloped windshield 16.Although shown in the upper portion of the instrument panel 10, it isunderstood that the doors 12 could also be formed in the front portionof the instrument panel 10, which constitutes a mid mount position.

[0041] As shown in cross-section in FIGS. 2 and 3, the panel structure10 has an exterior surface 10 a exposed to the vehicle interior and aninterior surface 10 b which is hidden from the vehicle interior when thepanel structure 10 is mounted in the automobile vehicle. The panelstructure 10 includes a rigid (or reinforcing) substrate 22 having onesurface defining the interior surface 10 b of the panel structure 10. Aportion of the substrate 22 defines the pivotal doors 12. Alternatively,the pivotal doors 12 can be formed separately from the substrate 22, andattached to the substrate 22 via, for example, hinges or the like (notshown). In the illustrated embodiment, when viewed from the backside ofthe substrate 22, the doors 12 define an H-pattern; however, it isunderstood that the doors 12 can define other patterns and can bedisplaced by other means (other than pivotal movement). For example,other possible patterns include X, C, U, and inverted U shapes.

[0042] The panel structure 10 further includes a layered compositestructure, generally designated by reference numeral 24 (FIG. 2),comprising an outer layer 26 having an outer surface 26 a defining atleast a portion of the exposed exterior surface 10 a (FIG. 4) of thepanel structure 10, a seam defining structure, namely a thin narrowelongated structure 27, and an inner layer 28. At least a portion of theouter layer 26 is exposed to the vehicle interior, while a portion ofthe outer layer 26 may be hidden from view by a decorative or othermasking item. An intermediate layer 30 comprising a relatively rigid (orsemi-rigid) polyurethane cellular foam is interposed between the layeredcomposite structure 24 and the substrate 22.

[0043] The inner layer 28, which is relatively thick in comparison tothe outer layer 26, has an outer surface adjacent to both a portion ofan inner surface 26 b of the outer layer 26 and the narrow elongatedstructure 27. Preferably, the inner layer is interfacially chemicallybonded with the outer layer 26. The narrow elongated structure 27preferably has a shape that substantially corresponds to the shape ofthe edges of the doors 12 that part from the substrate 22 duringpivoting movement of the doors 12 (e.g., an H-shape in the illustrativeembodiment). Generally, the narrow elongated structure 27 can be made ofa material having a lower tensile strength than that of the inner layer28. Preferably, the tensile strength of the narrow elongated structure27 is about 50% lower than that of the inner layer 28, thus defining afrangible line or an inherent line of weakness. The density and/ortensile strength of the elongated structure 27 can be lowered byincluding silica, glass beads, talc, and other fillers, and/or by addingblowing agents, such as azo-blowing agents, into the elongated structure27. The elongated structure 27 is made of or coated with a materialwhich is chemically and adhesively compatible with the material of theinner layer 28.

[0044] In the illustrated embodiment of FIG. 3, an air bag deploymentsystem 40 used in combination with this invention can include anyconventional system disposable behind a panel-like structure and capableof deploying an air bag 42 at an adequate rate to protect the vehicleoccupants. A typical system 40 can include, for example, a stationarygas generator or canister 44 situated in a housing 46 mounted on asuitable vehicle component (not shown). When the vehicle is impacted, animpact sensor 48 actuates the gas generator 44, causing the gasgenerator 44 to condition a controller 49 to initiate gas generation andexpel a suitable inflatant gas into the air bag 42.

[0045] As shown in FIGS. 3 and 4, as the air bag 42 is inflated from itsfolded, undeployed state to a fully inflated, deployed state, theexpanding air bag 42 impacts against the backside of the panel structure10. The force of the impact displaces the doors 12 into the passengers'compartment of the vehicle and thereby fractures the composite structure24 along the narrow elongated structure 27 to create a passageway(unnumbered). The formed passageway permits expansion of the air bag 42into the passengers' compartment of the vehicle and protects theoccupants from violent collision against the panel structure 10 orwindshield 16.

[0046] As shown in FIG. 5, the method of this first embodiment isgenerally described in U.S. Pat. No. 5,885,662 and utilizes a first moldcomponent or part 50 having a first mold surface 52. The first moldcomponent 50 preferably is formulated by electrolytically depositingnickel over a rigid cast epoxy substrate which is secondarily removed atthe end of the deposition/plating process to yield a self-supportingmold capable of being mounted and controlled in a tooling module. Thefirst mold surface 52 has a complementary configuration to the desiredconfiguration of the outer layer 26, and is grained to define a texturethat substantially complements the desired texture of the outer layer 26and simulates real leather.

[0047]FIG. 5 illustrates the first step in this embodiment in which theouter layer 26 is obtained by applying, preferably by spraying, awater-dispersed composition 54 onto the first mold surface 52. Thewater-dispersed composition 54 comprises at least one light-stablealiphatic thermoplastic polyurethane containing one or more pendenthydroxyl and/or carboxyl functional groups, at least one desiredcoloring agent, and at least one heat-activated crosslinker. Suitablecrosslinkers include blocked, heat-activated aliphatic diisocyanates,carbodiimide (H_N═C═N_H), also known as cyanamide, and compounds havinga plurality of aziridine groups. The average molecular weight of thethermoplastic polyurethane can be in a range of from about 5000 to about7000, and more preferably about 6000. An exemplary thermoplasticpolyurethane and blocked, heat-activated aliphatic diisocyanate can beobtained from Titan Finishes Corp. of Detroit, Mich. under the tradedesignation PROTOTHANE WR, WATER BASED IN-MOLD COATING. The aliphaticdiisocyanate may be cyclic or non-cyclic, but should be light stable. Asreferred to herein, diisocyanates also encompasses prepolymers havingtwo _NCO groups which are reactive with the thermoplastic polyurethane.An exemplary aliphatic diisocyanate is hexamethylene diisocyanate (HMI),which is available from Bayer, Rhone Poulenc, and Nippon Polyurethane.An exemplary water-dispersed composition comprising a thermoplasticpolyurethane and carbodiimide can be obtained from C.F. Jameson &Company, Inc. of Bradford, Mass. under the trade designation JAMESON WVFSERIES FLEXCOAT IMC. The desired weight ratio of thermoplasticpolyurethane to crosslinker for these particular compositions is about 8to 1 by volume (equivalent ratio of 1.44 thermoplastic polyurethane to1.08 crosslinker on a dry basis).

[0048] The water-dispersed composition 54 can be prepared by providingthe thermoplastic polyurethane component as a colloidal solution in asolvent such as N-methyl pyrrolidone, then dispersing the solution byadding water, the coloring agent, and conventional additives, ifdesired. Sufficient water (e.g., about 61.1% by weight) can be added sothat the solvent concentration in the water-dispersed composition 54 is,for example, about 8.1% by weight before drying.

[0049] The optional additives in the water-dispersed composition 54 caninclude, without limitation, any combination of the following: heat andultra-violet light stabilizers, pH stabilizers to maintain an alkalinestate of dispersion, plasticizers, antioxidants, dulling agents,surfactants, colloidal protectants to maintain particles in suspension,carbon black, thixotropic agents (e.g., hydroxy methyl cellulose), andfillers such as clay particles.

[0050] The water-dispersed composition 54 can contain, for example,about 25% to about 35% solids by weight, and more preferably about 29%solids by weight, about 10% to about 80% water by weight, and morepreferably about 61% water by weight, and about 6% to 10% solvents byweight, depending on desired color and additives. An insufficient amountof water in the composition 54 can adversely affect the viscosity of thecomposition 54 and thus adversely affect the application of thewater-dispersed composition 54 onto the first mold surface 52. On theother hand, an excess amount of water in the water-dispersed composition54 can alter the sprayability and coating efficiency of thewater-dispersed composition 54.

[0051] To the thermoplastic polyurethane solution may be added asolution of the blocked, heat-activated aliphatic diisocyanate, whichcan include as a solvent, for example, 1-methyl-2-pyrrolidine and/or4-hydroxy-4-methyl-2-pentanone. A discussion of blocked isocyanates isincluded in Practical Chemistry of Polyurethanes and Diisocyanates,Akron Polymer Laboratories, David Russell (1991), the completedisclosure of which is incorporated herein by reference. The blocked,heat-activated aliphatic diisocyanate is preferably maintained at roomtemperature and protected from heat until use. When influenced by theheat, such as the heat of the tooling during spraying application, theblocked, heat-activated aliphatic diisocyanate reacts with the hydroxyland/or carboxyl groups of the thermoplastic polyurethane to crosslinkthe thermoplastic polyurethane with itself or with polyol constituentsof the rapidly reacting composition.

[0052] Alternatively, the water-dispersed composition 54 can be preparedby adding to the thermoplastic polyurethane solution a solutioncomprising the carbodiimide, which can include, for example, glycolether acetate and/or xylene as the solvent.

[0053] The water-dispersed composition 54 can be prepared by withdrawingthe light-stable thermoplastic polyurethane and the heat-activatedcrosslinker from separate storage chambers in continuous, meteredstreams, and mixing these constituents immediately prior to contact withthe first mold surface 52. Alternatively, the light-stable aliphaticthermoplastic polyurethane and the crosslinker constituents can bestably premixed, or “hot-potted”, for up to about 24 hours at roomtemperature before application. This technique is known as “hot-potting”since the thermoplastic polyurethane and crosslinker slowly react witheach other at room temperature in a spray pressure pot. If the admixtureis hot-potted for more than about 24 hours at room temperature beforeapplication of the water-dispersed composition 54 onto the first moldsurface 52, the resulting crosslinked light-stable polyurethane exhibitsinferior solvent and wear resistance properties and extensibility andmay not provide an idealized bond to the inner layer 28. Thewater-dispersed composition 54 may be formed from a colloidal solutionof resin particles, which is added to water to disperse the resinparticles in the water.

[0054] Application of the water-dispersed composition 54 onto the heatedfirst mold surface 52 induces chemical reaction between the pendenthydroxyl and/or carboxyl functional groups of the light-stablethermoplastic polyurethane and the heat-activated crosslinker to therebyproduce a partially crosslinked light-stable polyurethane. The firstmold surface 52 should be heated to a sufficient temperature to drivethe crosslinking reaction, but should not be so high as to causedelamination of the composition 54 from the mold surface 52. Preferably,the first mold surface 52 is heated to a temperature in a range of fromabout 60EC (140EF) to about 71.1EC (160EF). The heating of the firstmold surface 52 to such elevated temperatures prior to application ofthe water-dispersed composition 54 thereto also serves to melt anddisperse semi-permanent mold releasing agents, such as microcrystallinewax mold releasing agents, applied to the first mold surface 52. Theheated mold surface 52 evaporates the wax dispersants and leaves a thinresidue that does not collect in the intricate grain detail of the firstmold surface 52.

[0055] Once the crosslinked light-stable polyurethane has been formed onthe first mold surface 52, the water-dispersed composition 54 issubstantially dried while being retained on the first mold surface 52 toobtain the outer layer 26. As shown in FIG. 6, the partially crosslinkedlight-stable polyurethane can be subjected to a heat source 56 to induceevaporation of the water and solvent therefrom and coalesce the resinparticles to form the outer layer 26 with the outer surface 26 aadjacent to the first mold surface 52. Although not shown in FIG. 6,such heat source 56 is preferably integrated with the first mold 50, andpreferably heats the first mold surface 52 to an elevated temperature ofabout 65.6EC (150EF) or higher. At least a portion of the outer surface26 a of the outer layer 26 has the desired touch, color, and grain-likeconfiguration of the panel-like structure 10.

[0056] Generally, the outer layer 26 has a thickness in a range of fromabout 0.0025 cm to about 0.0038 cm (that is, from about 0.001 inch toabout 0.0015 inch; or from about 1.0 mils to about 1.5 mils). Theparticular coloring agent selected can directly influence the desiredthickness of the outer layer 26. Darker colors, such as grays andbrowns, usually only require a relatively small film thickness to maskthe color of the hidden elongated structure 27 and the inner layer 28,whereas lighter colors such as reds and blues usually dictate theprovision of a relatively larger thickness to obtain an opaque,non-transparent outer layer 26 that conceals the structure 27 and theelongated inner layer 28 from view.

[0057] In accordance with a variant of the present invention, the outerlayer 26 can exhibit a dualtone or multitone appearance. This variantembodiment can be accomplished, for example, by abrasive treatment of aportion of the mold surface of the tooling. The greater the amount ofabrasive treatment, the duller the appearance of the outer layer 26. Adualtone appearance can be especially desirable for instrument panels,since the upper region of an instrument panel generally should have alow gloss in order to reduce reflectance and veiling glare.

[0058] A secondary or alternative heat source can be applied foractivating the reaction between the light-stable thermoplasticpolyurethane and the crosslinker. For example, the water-dispersedcomposition 54 can be preheated before being applied to the first moldsurface 52, such that the first mold surface 52 does not have to beheated to initiate the reaction between the crosslinker and thelight-stable thermoplastic polyurethane.

[0059] Referring to FIGS. 7 and 8, there are shown differentconstructions and arrangements of the seam defining structure. As shownin FIG. 7, according to one embodiment the narrow elongated structure 27a may be a strip of film, and may be made from, by way of example, athermoplastic material, including, by way of example, a polyester,polyurethane, and/or polyamide (nylon). In one preferred embodiment, theelongated structure 27 is made of MYLAR. The width of the tape may be onthe order of from about 2 mm to about 3 mm, and its thickness may be onthe order of from about 0.1 mm to about 0.2 mm.

[0060] As shown in FIG. 8, the seam defining structure may be in theform of a string or twine. The string or twine may be, for example, fromabout 1 mm to about 1.5 mm in diameter. Any material that is capable ofbeing formed into a twined configuration to create a disruption into thestructure, without introducing a foreign entity that will cause thestring or twine to significantly expand or contract over time that mightcause “read-through”, may be used. Materials that are similar to thoseselected for the inner layer are preferred. The physical properties,including extensibility, of the twine or string (or the elongated strip)may be selected to cause tearing in the twine or string (or theelongated strip) and/or at the interface of the twine or string (or theelongated strip) and the inner layer 28 in a controlled and predictableway. Accordingly, the twine or string material 27 b (or elongated strip27 a) may be non-homogenous, and may have a lesser or greater tensilestrength than the inner layer 28. However, the elongated structure 27should be made of a material that, during and after deployment, will notfragment or be sufficiently stiff to injure the driver or passenger.

[0061] Returning to the process, as shown in FIG. 9, the narrowelongated structure 27 is applied onto the inner surface 26 b of theouter layer 26. The elongated structure 27 is positioned and configuredto define an exteriorly invisible tear seam generally corresponding witha portion of an outline of the doors 12 movable through the layeredcomposite structure 24 during the operation of the secondary restraintsystem 40. Next, an inner layer 28 is deposited over the inner surface26 b of the outer layer 26 and the thin narrow elongated structure 27applied thereto while the outer layer 26 is retained on the first moldsurface 52 in a substantially dry state. The thin narrow elongatedstructure 27 adheres to the inner layer 28. The adhesive bond betweenthe elongated structure 27 is inherently less than the interfacial bondbetween inner layer 28 and outer layer 26 creating a frangible line inthe inner layer 28 along the exteriorly invisible tear seam.

[0062] Next, the polyurethane elastomer inner layer 28, as is alsodepicted in FIG. 9, is formed by spraying a rapidly reacting compositiononto the inner surface 26 b of the outer layer 26 while the outer layer26 is retained on the first mold surface 52 in a substantially drystate.

[0063] It is to be understood that the above-discussed sequence ofapplying the narrow elongated structure 27 and the inner layer 28 may bereversed or modified. For example, in one alternative embodiment a firstportion of the inner layer 28 is applied onto the inner surface 26 b ofthe outer layer 26 while the outer layer 26 is on the mold surface 52,but before the narrow elongated structure 27 has been applied thereto.The narrow elongated structure 27 is then applied onto the first portionof the inner layer 28 while the first portion is still tacky so that theelongated structure 27 is spaced from the inner surface 26 b of theouter layer 28, thereby decreasing the likelihood of “read-through” ofthe pattern of the elongated structure 27. A second portion of the innerlayer 28 is then applied over both the first portion of the inner layer28 and the narrow elongated structure 27 applied thereto while the outerlayer 26 is on the mold surface 52. The second portion of the innerlayer 28 can be applied in such a thickness so that the elongatedstructure 27 is partially exposed or completely encapsulated by theinner layer 28.

[0064] In another alternative method, the inner layer 28 is applied onthe inner surface 26 b of the outer layer 26 while the outer layer 26 ison the mold surface 52, but before the narrow elongated structure 27 hasbeen applied thereto. The narrow elongated structure 27 is then appliedon an inner surface 28 b of the inner layer 28 (while the inner layer 28is still tacky and not fully reacted, i.e. in a reactive state) andpressed into the inner layer 28 to embed the narrow elongated structure27 in the inner layer 28 and create, by virtue of the presence of theembedded narrow elongated structure 27, the exteriorly invisible tearseam. Again, spacing the narrow elongated structure 27 from the innersurface 26 b of the outer layer 26 decreases the chance of read-through.

[0065] The inner layer 28 can be made from one or more base polymersthat can be sprayed or cast by conventional techniques. Suitable basepolymers include, for example and without limitation, PVC, thermoplasticpolyurethanes, thermoplastic polyolefins, thermoplastic elastomers, andany combination thereof. The composition for forming the inner layer 28can also contain one or more additives. Preferably, at least one of thebase polymers and/or the additives is highly reactive with unreacted,residual functional groups of the crosslinker in the outer layer 26 thathave not reacted with the pendent functional groups of the polyurethaneof the outer layer 26. Unreacted functional groups of the crosslinkerpenetrate into the inner layer 28 and provide reactive sites forcrosslinking the polyurethane of the outer layer 26 with the inner layer28. An interfacial chemical bond between the inner surface 26 b of theouter layer 26 and the adjacent outer surface 28 a of the inner layer 28can thereby be formed. The layered composite structure 24 is thusobtained. If the crosslinking is performed under optimum crosslinkingconditions, the boundary between the outer and inner layers 26 and 28about the seam defining structure of the layered composite structure 24can become visually indistinct, such that a transition phase appears atthe interface of the two layers. As referred to herein, interfacialchemical bonding encompasses, but is not limited to, such crosslinkingreactions in which the interfacial boundary between the outer and innerlayers 26 and 28 is visually indistinct and the layers 26 and 28 areinseparable.

[0066] In a preferred embodiment, the inner layer 28 is prepared from apolyurethane elastomer, and even more preferably from an aromaticpolyurethane elastomer. The polyurethane elastomer inner layer 28 may beformed by spraying a rapidly reacting composition onto the inner surface26 b of the outer layer 26 and optionally the elongated structure 27,which are retained on the first mold surface 52 in a substantially drystate. The rapidly reacting composition preferably contains at least onearomatic polyisocyanate and at least one polyol, which react with eachother to form the non-light-stable polyurethane elastomeric inner layer28. As referred to herein, the term elastomer encompasses a resilientpolymer composition stretchable under moderate tension and compressibleand having a relatively high tensile strength and memory so that, uponrelease of the tension, the elastomer retracts into and recovers itsoriginal dimensions or dimensions substantially similar to its originaldimensions.

[0067] In addition to being reactive with the polyisocyanate, the polyolof the rapidly reacting composition can contain one or more pendenthydroxyl and/or carboxyl functional groups that are highly reactive withunreacted functional groups of the crosslinker, which is preferably ablocked, heat-activated aliphatic diisocyanate, in the outer layer 26that have not reacted with the pendent functional groups of thepolyurethane of the outer layer 26. Unreacted functional groups of theblocked, heat-activated light-stable diisocyanate penetrate into theinner layer 28 and react with the pendent functional groups of thepolyol constituent. As a result, the blocked, heat-activatedlight-stable diisocyanate crosslinks the polyurethane of the outer layer26 with the polyurethane elastomer of the inner layer 28 and therebyforms an interfacial chemical bond between the inner surface 26 b of theouter layer 26 and the adjacent outer surface 28 a of the inner layer28. The layered composite structure 24 is thus obtained.

[0068] Generally, provisions should be taken to ensure that an adequateinterfacial chemical bond is achieved between the inner surface 26 b ofthe outer layer 26 and the adjacent outer surface 28 a of the innerlayer 28. For example, once the blocked, heat-activated light-stablediisocyanate is activated by heat, the crosslinking reaction between theheat-activated diisocyanate and the pendent hydroxyl and/or carboxylreactive groups of the thermoplastic polyurethane goes to completionwithin minutes, leaving the heat-activated light-stable diisocyanatewith substantially no residual reactive sites for crosslinking thepolyurethane of the outer layer 26 with the polyol of the rapidlyreacting composition. Therefore, the rapidly reacting compositiongenerally should be sprayed within six minutes, and preferably withintwo to four minutes, of completing the application of thewater-dispersed composition 54 to the first mold surface 52. Significantdelays in spraying the rapidly reacting composition also can cause theouter layer 26 to constrict and delaminate from the first mold surface52. As a consequence of delamination, the outer layer 26 will not have ashape complementary to the configuration of the first mold surface 52,and the entire composite 24 will have to be disposed of as scrap.

[0069] On the other hand, if the thermoplastic polyurethane of thewater-dispersed composition 54 is not given sufficient time to crosslinkbefore the rapidly reacting composition is sprayed thereon, the polyolcomponent of the rapidly reacting composition can undergo a condensationreaction with unreacted hydroxyl and/or carboxyl pendent functionalgroups of the polyurethane of the outer layer 26 to form ester or etherlinkages, respectively. While some formation of these linkages canadvantageously enhance the interfacial chemical bond, the condensationreactions release water, which in excess amounts can undesirablyincrease the cellularity of the inner layer 28 and interfere with theinterfacial chemical bond.

[0070] The interfacial chemical bond is further enhanced by separatelystoring the highly reactive polyol and aromatic polyisocyanatecomponents of the rapidly reacting composition in separate storagechambers and spraying these components on the inner surface 26 b of theouter layer 26 so as to avoid contact between these components untilspraying is conducted. A suitable dual nozzle spraying mechanism foraccomplishing this task is disclosed in U.S. Pat. Nos. 5,028,006 and5,071,683. By keeping these components separate until immediately priorto spraying, a portion of the polyol reacts with the heat-activatedaliphatic diisocyanate (and the hydroxyl and/or carboxyl pendentfunctional groups of the thermoplastic polyurethane) before all of thepolyol can completely react with the polyisocyanate.

[0071] Furthermore, given the hygroscopic nature of the aromaticpolyisocyanate component of the rapidly reacting composition, it isimportant that the outer layer 26 and the surrounding atmosphere (e.g.,humidity levels) be substantially dry during this spraying step in orderto obtain a strong interfacial chemical bond. While small amounts ofmoisture may be retained in the outer layer 26, the concentration ofsuch moisture should not be so great as to permit the water tosubstantially interfere with the reaction between the polyol andpolyisocyanate of the rapidly reacting composition. Undesirablereactions between the water and the polyisocyanate can disrupt thestoichiometric balance between the polyol and the polyisocyanate,leaving localized unreacted polyol deposits behind on the layeredcomposite structure 24. The water also can serve as a blowing agent,reacting with the polyisocyanate to release carbon dioxide which impartsa cellular structure to the inner layer 28. Excess amounts of water alsocan deleteriously interfere with the crosslinking reaction effected viathe polyol and the residual reactive sites of the blocked,heat-activated diisocyanate.

[0072] The rapidly reacting composition is preferably applied to theinner surface 26 a of the outer layer 26 at an elevated temperature toadvance these objectives. Suitable temperatures to which the first moldcomponent 52 can be heated range, by way of example and withoutlimitation, from about 60EC (140EF) to about 71.1EC (160EF).

[0073] As mentioned above, the inner layer 28 can also be formed bycasting, for example, a PVC or thermoplastic polyurethane castingcomposition. Suitable techniques and apparati for accomplishing castingare disclosed in the collection of WO 98/57790, U.S. Pat. No. 4,623,503,U.S. Pat. No. 4,621,995, U.S. Pat. No. 5,597,586, and U.S. Pat. No.4,217,325.

[0074] Generally, the inner layer 28 can have a thickness in a range offrom about 0.10 cm to about 0.15 cm (that is, from about 0.040 inch toabout 0.060 inch; or from about 40 mils to about 60 mils).

[0075] Aromatic Polyurethane Elastomer Inner Layer

[0076] Exemplary polyisocyanates that can be selected for forming theinner layer 28 include diisocyanates having aromatic closed-ringstructures, such as diphenylmethane diisocyanate prepolymer (MDIprepolymer), which can be obtained from BASF Corp. of Wyandotte, MI.under the trade designation ELASTOLIT M50555T, ISOCYANATE, NPU U05275,or diphenylmethane-4,4′-diisocyanate (MDI), or mixed isomers of MDI ormixtures of the above, which are available from BASF or Dow ChemicalCorp. of Midland, Mich., Mobay (Bayer) Chemical Corp. of Baytown, Tex.,or ICI America of Geismar, La. The above-mentioned non-light-stablearomatic polyisocyanates are very desirable for use in the inner layerin view of the higher rate of reactivity and completion of propertydevelopment and better physical properties (e.g., tensile strength,elongation, and tear strength) of these non-light-stable aromaticpolyisocyanate when compared to light-stable isocyanates such asisophorone diisocyanates, in which the —NCO groups are stericallyhindered due to their spatial arrangement at either end of the molecule.By contrast, the aromatic diisocyanates used in this inventionpreferably have —NCO groups directly attached to the aromatic ring. Inthis preferred embodiment, the aromatic diisocyanates yield faster ratesof reaction because of the arrangement and reactivity of the —NCO groupson the aromatic ring structure (e.g., in diphenylmethane diisocyanate)and the availability of the _NCO groups for reaction with the hydrogendonors of the _OH type residing on the organic chain of the polyols ofthe rapidly reacting composition.

[0077] Suitable polyols for this rapidly reacting composition include,without limitation, polyether polyols having average molecular weightsin a range of from about 200 to about 2000 and containing one or morependent hydroxyl and/or carboxyl groups in addition to primary hydroxylgroups, which can chemically react with unreacted functional —NCO groupsof the blocked, heat-activated aliphatic diisocyanate and the hydroxyland/or carboxyl pendent functional groups of the polyurethane of theouter layer 26. An exemplary polyol is ELASTOLIT M50555R NPU U05274 fromBASF Corp. of Wyandotte, Mich.

[0078] The rapidly reacting composition can also contain appropriateadditives, including, by way of example and without limitation, anycombination of the following: heat and ultra-violet light stabilizers,pH stabilizers, antioxidants, dulling agents, surfactants, carbon black,chain extenders (e.g., ethylene glycol), thixotropic agents (e.g.,amorphous silica), fillers such as clay particles, and catalysts such astin catalysts (e.g., dibutyltin dilaurate).

[0079] Non-Aromatic Polyurethane Elastomer Inner Layer

[0080] Exemplary polyisocyanates that can be selected for making theinner layer 28 include polyisocyanates having closed aliphatic ringstructures with pendent —NCO groups, such as isophorone diisocyanate,which can be obtained from Recticel under the tradename ISOFAST. Alsosuitable is tetramethyl xylene diisocyanate, which can be obtained fromTexaco under the tradename TMXDI.

[0081] Suitable polyols for this rapidly reacting composition include,without limitation, polyether polyols having molecular weights in arange of from about 220 to about 250 and containing one or more pendenthydroxyl and/or carboxyl groups (in addition to primary hydroxylgroups), which can chemically react with unreacted functional —NH groupsof the carbodiimide and the hydroxyl and/or carboxyl pendent functionalgroups of the polyurethane of the outer layer 26. An exemplary polyol isPOLYFAST from Recticel.

[0082] Additives as mentioned above in connection with the aromaticpolyurethane elastomer may be used for non-aromatic polyurethaneelastomer inner layers 28 as well.

[0083] Cast PVC Inner Layer

[0084] Where PVC is selected as the base polymer, the castingcomposition can include one or more plasticizers. In a preferredembodiment, the plasticizers selected for this invention are capable ofreacting with the crosslinker (e.g., carbodiimide) in the outer layer26, so that the crosslinker can successfully crosslink the polyurethaneof the outer layer 26 with the plasticizer of the casting composition.Exemplary plasticizers include, without limitation, plasticizers havingone or more pendent hydroxyl or carboxyl functional groups. Theseplasticizers are preferably incorporated around the backbone of the basepolymer as an internal lubricant.

[0085] Preferably, both a low molecular weight plasticizer and a mediummolecular weight plasticizer are included in the casting compositionhaving PVC as its base polymer. The low molecular weight plasticizer isselected to provide low temperature flexibility, so that performance ofthe inner layer 28 at low temperatures, such as _(—)30EC, is nothindered. An exemplary low molecular weight plasticizer isdi-2-ethylhexylphthalate (also known as DUP). On the other hand, themedium molecular weight plasticizer is selected to provide hightemperature stability to the inner layer 28. An exemplary mediummolecular weight plasticizer is trioctyltrimellitate (TOTM).

[0086] The amount of low molecular weight plasticizer should bemaintained fairly low so as to reduce volatilization and, consequently,window fogging. For example, the weight ratio of low molecular weightplasticizer to PVC base resin in the casting composition can be fromabout 0.25:100 to about 1:100. The weight ratio of medium molecularweight plasticizer to PVC base resin in the casting composition can bein a range of from about 10:100 to about 40:100, and more preferably ina range of from about 20:100 to about 40:100. If an insufficient amountof medium molecular weight plasticizer is used, the inner layer 28 maynot exhibit adequate high temperature aging properties, resulting in,for example, premature stiffening of the inner layer 28 after exposureto elevated temperatures. On the other hand, if an excess amount ofmedium molecular weight plasticizer is used, the article surface maytend to gloss at elevated temperatures, creating unacceptable surfacereflectance.

[0087] Where PVC is selected as the base polymer of the castingcomposition, the casting composition can be prepared by any suitabletechnique, including suspension or mass polymerization followed bydrying to provide a white, free-flowing powder of PVC having, forexample, an average particle size of about 350:m. The resulting PVCpowder can then be thoroughly mixed with the plasticizer to form thecasting composition by employing any suitable technique, such as highenergy compounding. During compounding, the plasticizer is absorbed bythe PVC and thereby causes the PVC to swell. Compounding can beperformed, for example, at a temperature in a range of from about 150EF(about 60EC) to about 190EC (about 88EC).

[0088] The plasticizer selected should impart thermal stability to thePVC powder and be permanent to render the article flexible for the lifeof the application. Generally, PVC powder consists of discrete particlegroups that, when subjected to excessive temperatures, decompose priorto melting. This decomposition liberates hydrogen chloride, whichautocatalytically degrades the PVC. Since the PVC is melted duringgelling and fusing steps, a suitable internal plasticizer is mixed withand absorbed in the PVC powder prior to casting in order to inhibitthermal degradation of the PVC and provide the inner layer 28 with asoft, flexible, compressing feel.

[0089] Preferably, the plasticizer is bound in the PVC matrix withsufficient bond energy to form a permanent part of the polymer matrixand thereby permit the finished fused article to exhibit goodflexibility and weathering at super- and sub-ambient conditions in use.

[0090] The casting composition having PVC as its base resin can containappropriate additives, including, by way of example and withoutlimitation, any combination of the following: heat and ultra-violetlight stabilizers, such as hydroquinones; internal lubricants, such asstearic acid; antioxidants; dulling agents; carbon black; and fillers,such as clay and/or diatomaceous earth. Other additives can also beintroduced into the inner layer 28 to protect against oxidation anddestabilization of the cast PVC. Such additives include barium, calcium,and zinc heat stabilizers, such as barium nonylphenate, calciumcarboxylate, and zinc stearate. These and other additives can beincluded to form the dry resin material by using, by way of example andwithout limitation, a high intensity dry powder mixer such as a Henschelmixer.

[0091] In addition, the PVC composition can comprise one or morecopolymer alloys or blends of PVC and another polymer, such as one ormore polyurethanes. Such copolymer alloys and blends can be prepared bytechniques well known to those skilled in the art, such as compounding.

[0092] Cast Thermoplastic Polyurethane Inner Layer

[0093] Where a thermoplastic polyurethane is selected as the basepolymer for the casting composition, the thermoplastic polyurethanepreferably contains at least one ethylenically unsaturated bond in itsbackbone and/or hydroxyl or carboxyl groups. In a preferred embodiment,the ethylenically unsaturated bond and/or hydroxyl groups of thethermoplastic polyurethane is/are capable of reacting with thecrosslinker (e.g., carbodiimide) in the outer layer 26, so that thecrosslinker can successfully crosslink the polyurethane of the outerlayer 26 with the polyurethane of the casting composition. Exemplarythermoplastic polyurethanes include, without limitation, ESTANE(provided by B. F. Goodrich of Akron, Ohio) and PELLETHANE (provided byDow Chemical Company of Midland Mich.).

[0094] The thermoplastic polyurethane of the casting composition can beprepared by, for example, a prepolymerization technique, followed bydrying, compounding, chopping, and grinding, to provide a free-flowingpowder of thermoplastic polyurethane. Excess polyols can be provided inpreparing the thermoplastic polyurethane of casting composition. Asmentioned above, the hydroxyl groups of the excess polyols can serve topromote crosslinking and the chemical bonding between the outer layer 26and the inner layer 28. The resulting thermoplastic polyurethane powdertypically has a brownish appearance, and can possess, for example, a 425mesh size. The powder can contain additives, as needed or required bythe intended use, to form the composition by employing any suitabletechnique, such as introducing the additives during prepolymerization.The weight ratio of the total additives to the base resin can be, forexample, in a range of from about 3:100 to about 7:100, depending on theintended use and additives included.

[0095] The casting composition including a thermoplastic polyurethane asits base polymer can contain appropriate additives, including, by way ofexample and without limitation, any combination of the following: heatstabilizers; flexibilizers, such as low molecular weight polyurethanes(incorporated into the backbone, for example, during the compounding orlike step); antioxidants; dulling agents; carbon black; fillers, such asclay particles; and free flowing additives. Other additives can also beintroduced into the inner layer 28 to protect against scorching. Theseand other additives can be included to form the dry resin material byusing, by way of example and without limitation, a high energyextruder/chopper.

[0096] In similar fashion, other thermoplastic powders based uponpolyolefins or elastomers may be formed. Extruded micropellets of thePVC, TPU, TPO, TPE, or other thermoplastic formulations or combinationsthereof may be cast instead of the powder form.

[0097] Various blends of polyether polyols and polyisocyanates havingsuitable resilience properties can be employed to form the semi-rigidpolyurethane cellular foam of the intermediate layer 30. For example,the polyisocyanate blend can include methylene diisocyanate. Thesemi-rigid polyurethane cellular foam also can contain appropriateadditives, including, by way of example and without limitation, anycombination of the following: surfactants, antioxidants, fillers,stabilizers, catalysts such as tin catalysts (e.g., dibutyl tindilaurate) and tertiary amines (e.g., diethanolamine), and small amountsof foaming agents such as water. In this regard, it is noted that thecondensation reaction between the blends of polyols and polyisocyanatesreleases water, which reacts with the polyisocyanate to generate carbondioxide and thereby impart the cellular structure to the intermediatelayer 30. Accordingly, a slightly stoichiometric excess of polyol can beprovided to form the semi-rigid polyurethane cellular foam.

[0098]FIG. 10 illustrates the next step of this embodiment, in which thelayered composite structure 24 is demolded (i.e., removed) from thefirst mold surface 52. The demolding process is often a relatively laborintensive, tedious, and time consuming task. Formation of tears in orundue stretching of the layered composite structure 24 during demoldingcan irreversibly ruin and thereby necessitate disposal of the layeredcomposite structure 24 as scrap. Such demolding problems andinefficiencies are largely overcome by practice of this invention, sincethe interfacial chemical bond between the outer layer 26 and inner layer28 strengthens the layered composite structure 24 by discouragingseparation of the outer and inner layer 26 and 28 and elongatedstructure 27 during demolding procedures. Moreover, such demoldingproblems and inefficiencies are further obviated by the use of thearomatic-based elastomer, since it has advantageous physical properties.

[0099] To enhance the releasibility from the first mold surface 52further, the mold surface 52 can be pretreated with a releasing agent.Exemplary releasing agents include, by way of example, high molecularweight microcrystalline wax mold releases, such as Chem-Trend PRC 7140,supplied by Chem-Trend, Inc. of Howell, Mich., or PRC 2006, alsosupplied by Chem-Trend. These mold releasing agents dry quickly on aheated mold within about 5 to about 10 seconds and form a releasebarrier between the grained mold surface 52 and the outer layer 26. Careshould be taken to avoid the accumulation of the mold releasing agent onthe first mold surface 52 or excess solids content in the agent, sincesuch accumulation or excess solids content tends to fill the intersticesof the decorative, grained mold surface 52, thereby removing from theexterior surface of the panel structure 10 the appearance of theintricate, hair-like grained configuration of the mold surface 52.Further, the use of excess mold releasing agents can cause the agents totransfer from the first mold surface 52 to the layered compositestructure 24 during demolding of the composite structure 24, thusrequiring additional wash-removal and drying steps after demolding andhence a loss in productivity.

[0100] After being demolded from the first mold surface 52, the layeredcomposite structure 24, including the combination of the outer and innerlayers 26 and 28 and narrow elongated structure 27, can be examined fordefects with a light source (not shown) while the layered compositestructure 24 is positioned on a transparent substrate (not shown). Suchdefects usually are present as cosmetic blemishes in the outer layer 26,and may include the presence of tears and rupturable portions lackingsufficient thickness to withstand stresses associated with demolding orthe further processing steps, especially the uniting step. If minor andisolated, such localized defects can be remedied by post application ofadditional water-dispersed composition 54 onto the outer layer 26.Additionally, minor tears or thin areas can be repaired usingthermoplastic, heat formable polyurethane tape on the backside 28 b ofthe layered composite structure 24. Advantageously, the need to scrapthe entire layered composite structure 24 is thereby averted. As acautionary note, however, post application spray repair of surface 26 ais generally undesirable and its use should be minimized to correctinglocalized defects, since post application spray repair can negate thegrained leather-like appearance of the outer surface 26 a of the outerlayer 26 which is transcribed from the first mold surface 52.

[0101] As discussed in further detail below, the steps of demolding andexamining of the layered composite structure 24 from the first moldsurface 52 are not required to be conducted immediately subsequent tothe formation of the layered composite structure 24. For example, thelayered composite structure 24 optionally can be maintained against thefirst mold surface 52 until completion of the panel structure 10.

[0102] Optionally, the layered composite structure 24 can be retained inthe first mold component 50 instead of being demolded and transferred toa second mold component 94 for the uniting step. Alternatively, thelayered composite structure 24 can be returned to the first moldcomponent 50 after being examined and treated.

[0103] After the layered composite structure 24 is demolded from thefirst mold surface 52 and examined, the layered composite structure 24is placed on a second mold surface 96 of a second mold part 94. As shownin FIG. 11, the second mold surface 96 is shaped to have a complementaryconfiguration to the outer layer 26. Then, a reactive mixture 98 forforming a semi-rigid cellular foam, such as a polyurethane semi-rigidcellular foam, is applied to an inner surface 28 b of the inner layer 28while the composite structure 24 is disposed on the second mold surface96 to form the intermediate layer 30. The reactive mixture 98 can beapplied, for instance, by employing high pressure impingement mixing anda mix-head nozzle. The second mold component 94 is generally heated to atemperature in a range of from about 35EC to about 45EC, and morepreferably in a range of from about 35EC to about 40EC, duringapplication of the reactive mixture 98. The mixture 98, which istypically relatively viscous, is in a transient state of reaction duringapplication to the second mold component 94 and begins to foam withinseconds of application.

[0104] Although the desired thickness of the intermediate layer ispartially dependent upon the intended use of the panel structure 10,generally the intermediate layer can have a thickness in a range of fromabout 5 mm to about 12 mm.

[0105] Once the reactive mixture 98 has been applied to the layeredcomposite structure 24 located on the second mold surface 96, a thirdcooperating mold part or component 100 carrying the pre-formed rigidsubstrate 22 having a doors 12 is moved into cooperating relation withthe second mold component 94, as shown in FIG. 12. The third moldcomponent 100 has a third mold surface 102 (FIG. 11) which iscomplementary to the interior surface 10 b of the panel structure 10.Thereafter, the reactive mixture 98 is foamed and cured, preferablyunder heat of approximately 43.3EC (10EF) and a self-generated cavitypressure of about 0.8 atm to form the intermediate layer 30. Thesemi-rigid polyurethane cellular foam serves to unite the layeredcomposite structure 24 with the pre-formed rigid substrate 22 disposedon the third mold surface 102. The panel structure including thecombination of the layered composite structure 24, the rigid substrate22, and the intermediate layer 30 then can be removed from the moldparts 94 and 100 and additional components can be affixed.

[0106] The rigid substrate 22 may be formed from any material possessingthe requisite strength to reinforce and mount the outer layer 26, innerlayer 28, and intermediate layer 30. Suitable materials include anymaterial with sufficient rigidity to permit the composite to be mountedinto a vehicular sub-structure, including, by way of example, injectionmolded thermoplastics, such as, without limitation, a styrene maleicanhydride (SMA), acrylonitrile butadiene styrene (ABS), polycarbonates(PC), an alloy of ABS-PC, reinforced reaction injection moldedpolyurethanes (RRIM), metals, metal alloys, wood-fiber composites, orany combination thereof. Fillers can be used in the substrate 22, as isknown in the art.

[0107] The reinforcing substrate 22 may optionally also includereinforcement nanoparticles comprising platelet minerals dispersed inthe desired polymer in desired ratios. The components can be blended bygeneral techniques known to those skilled in the art. For example, thecomponents can be blended and then melted in mixers or extruders.

[0108] The illustrated embodiment of this invention can also be modifiedby applying the reactive mixture 98 for forming the polyurethanesemi-rigid cellular foam 30 to the surface of the rigid substrate 22instead of the layered composite structure 24. Alternatively, the secondand third mold components 94 and 100 can be cooperatively engaged todefine a cavity between the inner surface 28 b of the inner layer 28 andthe outer surface of the substrate 22, with the reactive mixture 98thereafter being injected between the rigid substrate 22 and thecomposite structure 24.

[0109] Additional specific preferred methods, for the purposes of thisinvention, for forming a polymer composite having dispersed thereinexfoliated layered particles are disclosed in U.S. Pat. Nos. 5,717,000,5,747,560, 5,698,624, and WO 93/11190. For additional background thefollowing are also references: U.S. Pat. Nos. 4,739,007 and 5,652,284.

[0110] Where the doors separate from each other during deployment of theair bag, the doors can be attached to the substrate with hingecomponents or tether devices to ensure that the doors do not becomeprojectiles during actuation of the air bag assembly. Suitableconnecting means and arrangements for practice in this invention aredisclosed in U.S. Pat. Nos. 5,456,490, 5,222,760, 5,569,959, and5,560,646. Where the doors are integrally molded, the doors can bereinforced at the hinged or tethered areas.

[0111] The second embodiment of this invention will now be describedwith reference to FIGS. 13-17. In describing the second embodiment,identical reference numerals to those used in FIGS. 1-12 will be used todescribe structures and parts having similar properties or functions tothose of the first embodiment. For the purpose of brevity, steps andfeatures involved in the second embodiment that are the same as thosedescribed above in connection with the first embodiment will not berepeated hereinbelow.

[0112] Referring now more particularly to the drawings, and inparticular FIGS. 13 and 14, in accordance with this second embodiment,the layered composite structure 24 comprises the outer layer 26 and theinner layer 28, and a seam defining structure, namely a thin sheetstructure 29 interposed therebetween (or partially or fully embeddedwithin the inner layer 28). The thin sheet structure 29 overlays aportion of the outer layer 26 corresponding to the portion of thelayered composite structure 24 through which the doors 12 move duringthe operation of the secondary restraint system 40. The thin sheetstructure 29 is severed in a position and configuration to define anexteriorly invisible tear seam generally conforming to a portion of theoutline of the movable doors 12.

[0113] During deployment of the air bag 42, the expanding air bag 42impacts against the backside of the panel structure 10 and fractures thecomposite structure 24 along the severed portion of the thin sheetstructure 29 to create a passageway. The formed passageway permitsexpansion of the air bag 42 into the passengers' compartment of thevehicle and protects the occupants from violent collision against thepanel structure 10 or windshield 16.

[0114] Referring to FIGS. 15 and 16, there are shown two constructionsof the thin sheet structure 29 with an H-shaped pattern 31 severedtherein. The pattern should correspond to the movable portion of thedoors 12. The thin sheet structure 29 is severed in a position andconfiguration to define an exteriorly invisible tear seam generallyconforming to an outline of the movable doors 12. As referred to herein,severing includes the formation of continuous or non-continuous cuts orperforations or channels (having a width), and cuts or perforations orchannels that pierce all or only a portion of the thickness of the thinsheet structure 29.

[0115] As shown in FIG. 15, the sheet structure 29 is constructed as acontinuous sheet, which may be made of a thermoplastic material. Amongthe materials suitable for preparing the continuous sheet structure 29are MYLAR polyester, polyurethane, or polyamide (Nylon) film withadhesive backing to self-adhere to the outer layer 26 while thepolyurethane elastomer inner layer 28 is applied. The size of the sheet29 may be, for example, on the order of 30 mm by 38 mm, with a thicknesson the order of from about 0.1 mm to about 0.2 mm. The pattern of thesevered film depends on the configuration of the outline of the doors12.

[0116] As shown in FIG. 16, alternatively the sheet structure 29 may beformed from a mesh with a severed portion, designated by referencenumeral 31. The mesh (or a porous layer) is advantageous inasmuch as itcontains voids through which the outer and inner layer 26 and 28 maycontact and undergo interfacial chemical bonding. It has even beenobserved that during deposition of the inner layer 28, the mesh sheetstructure 29 may be lifted from the surface 26 b of the outer layer 26and encapsulated in the inner layer 28. The mesh may be made ofspunbonded polyester (available from Reemay located in Old Hickory,Tenn.) or fiberglass mesh or polyester non-woven cloth, to name a fewexamples. The mesh should have a heat-activated adhesive coupling agentcompatible to bond with the inner layer 28 and so as to maintain themesh in place during the application of the inner layer 28. The meshsheet 29 may have dimensions on the order of from about 30 mm to about38 mm with a thickness in a range of from about 0.1 mm to about 0.2 mm.

[0117] The thin sheet structure 29 applied to the inner surface 26 b ofthe outer layer 26 and replaces the elongated structure 27 and theprocess steps associated therewith. Otherwise, the process steps areidentical with the first embodiment.

[0118] The thin sheet structure 29 is substantially larger than the areaof the opening through which the doors 12 egress, but may have a lesserwidth and height than the inner and outer layers 26 and 28. As with thefirst embodiment, the inner layer 28 may be formed from a variety ofdifferent base polymers and additives; however, the use of apolyurethane elastomer, especially an aromatic polyurethane elastomer,is preferred.

[0119] In another alternative method as illustrated in FIG. 18, thesheet structure 29 is provided with peripheral walls that extendperpendicular from the plane of the sheet structure 29 so as to definean open ended box. The peripheral walls face away from the first moldsurface 52 and protrude from the inner surface 28 b of the inner layer28. The protruding portions of the peripheral walls are attached tosubstrate 22. The attachment of the sheet structure 29 to the substrate22 localizes elongation of the outer and inner layers 26 and 28 (causedduring movement of the doors 12 through the layered composite structure24) to those portions of the layers 26 and 28 located within the areadefined by the peripheral walls of the sheet structure 29. As aconsequence, the portions of the layered composite structure 24 locatedoutside of the area defined by the peripheral walls of the sheetstructure 29 are not subjected to excess elongation and are less likelyto separate from the rigid substrate 22 and the optional cellular foam30. This embodiment is especially useful for panel designs that do notprovide sufficient area of support for the layered composite structure24, permitting the sheet structure 29 to be self-restraining (relativeto the layered composite structure 24) during airbag deployment.

[0120] Although the method of this invention has been embodied above inconnection with the preparation of a instrument panel, it is understoodthat the method is equally applicable to other panel structures,including for example door panels, interior rear quarter panels, pillarcovers and headliners.

[0121] The foregoing detailed description of the preferred embodimentsof the invention has been provided for the purpose of explaining theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications as are suited to theparticular use contemplated. The foregoing detailed description is notintended to be exhaustive or to limit the invention to the preciseembodiments disclosed. Modifications and equivalents will be apparent topractitioners skilled in this art and are encompassed within the scopeof the appended claims.

What is claimed is:
 1. A process for making a layered compositestructure for a panel structure mountable in a vehicle to part of theinterior thereof in concealing relation to a secondary restraint system,said process comprising: forming on a mold surface the layered compositestructure comprising an outer layer defining at least a portion of anexterior surface of the panel structure, an inner layer adjacent theouter, said inner layer including a seam defining structure adhered tothe inner layer defining a frangible line of an invisible tear seamcorresponding with the secondary restraint system.
 2. A process asdefined in claim 1, wherein said forming of the layered compositestructure comprises: establishing the outer layer on the mold surface soas to have a configuration complementary to mold surface; applying theseam defining structure on the inner surface of the outer layer whilethe outer layer is on the mold surface; and applying the inner layerover the inner surface of the outer layer and the seam definingstructure applied thereto while the outer layer is on the mold surfaceto adhere the outer layer thereto.
 3. A process as defined in claim 1,wherein said forming of the layered composite structure comprises:establishing the outer layer on the mold surface so as to have aconfiguration complementary to the mold surface; applying a firstportion of the inner layer on the inner surface of the outer layer whilethe outer layer is on the mold surface to adhere the outer layerthereto; applying the seam defining structure on the inner surface ofthe first portion of the inner layer while the outer layer is on themold surface and positioning the narrow seam defining structure todefine the exteriorly invisible tear seam; and applying a second portionof the inner layer over the inner surface of the first portion of theinner layer and the seam defining structure applied thereto while theouter layer is on the mold surface.
 4. A process as defined in claim 1,wherein said forming of the layered composite structure comprises:establishing the outer layer on the mold surface so as to have aconfiguration complementary to the mold surface; applying the innerlayer on the inner surface of the outer layer while the outer layer ison the mold surface to adhere the outer layer thereto; applying the seamdefining structure on an inner surface of the inner layer while theouter layer is on the mold surface; and pressing the narrow seamdefining structure into the inner layer while the inner layer is in areactive state to embed the seam defining structure in the inner layer.5. A process as defined in claims 2 to 4, wherein the seam definingstructure comprises a thermoplastic material.
 6. A process defined inclaims 2 to 4, wherein the seam defining structure comprises a sheetstructure.
 7. A process as defined in claim 6, wherein the sheetstructure comprises an open mesh fabric.
 8. A process as defined inclaim 7, where in the open mesh fabric comprises a fiber glass mattreated with an adhesive coupling agent compatible to bond with theinner layer.
 9. A process as defined in claims 7 or 8 wherein said sheetstructure is severed along said frangible line.
 10. A process as definedin claim 9, wherein the severed sheet structure comprises peripheralwalls surrounding the invisible tear seam and protruding from the innerlayer away from the outer layer.
 11. A process as defined in claims 2 to4, wherein the seam defining structure comprises twine.
 12. A processaccording to claims 5, 6 or 11, wherein said establishing of the outerlayer on the mold surface comprises: applying a water-dispersedcomposition onto the mold surface, the water-dispersed compositioncomprising at least one light-stable thermoplastic polyurethane, atleast one coloring agent, and at least one heat-activated crosslinker,applying sufficient heat to induce partial crosslinking of thelight-stable thermoplastic polyurethane with the crosslinker, andsubstantially drying the water-dispersed composition while on the moldsurface so as to establish the outer layer; and the inner layer isformed by applying a composition onto an inner surface of the outerlayer and, crosslinking the inner layer which extends about the seamdefining structure with the polyurethane of the outer layer via residualunreacted functional groups of the crosslinker to form interfacialchemical bonding between the inner surface of the outer layer and anadjacent surface of the inner layer.
 13. A process according to claim12, wherein the outer layer has a thickness in a range of from about0.0025 cm to about 0.0038 cm.
 14. A process according to claim 13,wherein the inner layer has a thickness in a range of from about 0.10 cmto about 0.15 cm.
 15. A process according to claim 12, wherein the moldsurface has a complementary configuration to an exterior surface of adoor panel.
 16. A process according to claim 12, wherein the moldsurface has a complementary configuration to an exterior surface of aninstrument panel.
 17. A process according to claim 12, wherein thecomposition from which the inner layer is formed comprises an aromaticpolyisocyanate, and wherein the crosslinker is a blocked, heat-activateddiisocyanate.
 18. A process according to any one of the preceding claimswherein the process further comprises a step of uniting the layeredcomposite structure after the formation thereof with a reinforcingsubstrate so that the reinforcing substrate reinforces the layeredcomposite structure in such a way that the layered composite structurefractures generally along the tear seam in response to the operation ofthe secondary restraint system.
 19. A process as defined in claim 18,wherein said uniting of the layered composite structure with thereinforcing substrate comprises placing a rapid reacting mixture betweenthe layered composite structure and the reinforcing substrate andforming a cellular polyurethane foam therefrom.
 20. A layered compositestructure for a panel structure mountable in a vehicle to form a part ofthe interior thereof, said panel structure having an exterior surfaceexposed to the vehicle interior and an interior surface disposed incooperating and concealing relation with a secondary restraint system,said layered composite structure comprising: an outer layer with anopaque visual appearance defining an exposed exterior surface of saidpanel structure; and an inner layer adhered to an inner surface of saidouter layer and including an adhesively bonded seam defining structure,said seam defining structure defining a frangible line corresponding toan invisible tear seam which fractures in response to operation of thesecondary restraint system.
 21. A layered composite structure as definedin claim 20, wherein the seam defining structure comprises athermoplastic material.
 22. A layered composite structure defined inclaim 20, wherein the seam defining structure comprises a sheetstructure.
 23. A layered composite structure as defined in claim 22,wherein the sheet structure comprises an open mesh fabric.
 24. A layeredcomposite structure as defined in claim 23, where in the open meshfabric comprises a fiber glass mat.
 25. A layered composite structure asdefined in claims 22, 23 or 24 wherein said sheet structure is severedalong said line.
 26. A layered composite structure as defined in claim25, wherein the severed sheet structure comprises peripheral wallssurrounding the invisible tear seam and protruding from the inner layeraway from the outer layer.
 27. A layered composite structure as definedin claim 20, wherein the seam defining structure comprises twine.
 28. Alayered composite structure according to claims 21, 22 or 27, whereinsaid outer layer comprises: a water-dispersed composition comprising atleast one light-stable thermoplastic polyurethane, at least one coloringagent, and at least one heat-activated crosslinker; and the inner layeris a composition which crosslinks the inner layer about the seamdefining structure with the polyurethane of the outer layer via residualunreacted functional groups of the crosslinker to form interfacialchemical bonding between the inner surface of the outer layer and anadjacent surface of the inner layer.
 29. A layered composite structureaccording to claim 28, wherein the outer layer has a thickness in arange of from about 0.0025 cm to about 0.0038 cm.
 30. A layeredcomposite structure according to claim 29, wherein the inner layer has athickness in a range of from about 0.10 cm to about 0.15 cm.
 31. Alayered composite structure according to claim 28, wherein the layeredcomposite structure has a configuration of an exterior surface of a doorpanel.
 32. A layered composite structure according to claim 28, whereinthe layered composite structure has a configuration of an exteriorsurface of an instrument panel.
 33. A layered composite structureaccording to claim 28, wherein the composition from which the innerlayer is formed comprises an aromatic polyisocyanate, and wherein thecrosslinker is a blocked, heat-activated diisocyanate.
 34. A layeredcomposite structure according to any one of the preceding claims whereinthe layered composite structure is united with a reinforcing substrateso that the reinforcing substrate reinforces the layered compositestructure in such a way that the layered composite structure fracturesgenerally along the tear seam in response to the operation of thesecondary restraint system.
 35. A layered composite structure as definedin claim 34, wherein a rapid reacting mixture which forms a cellularpolyurethane foam unites the layered composite structure and thereinforcing substrate and therefrom.